This invention pertains generally to microwave power combiners or dividers and particularly to planar, broadband power combiners or dividers suitable for either stripline of microstrip with any number of terminations.
As is known in the art, amplifiers using Field Effect Transistors (FETs) are becoming increasingly attractive for use as microwave power sources because of the relatively broad bandwidth attainable with such transistors. FETs to date have, however, been power limited, with devices capable of delivering 1 watt of output power at X-band only recently becoming available. In a typical application where a solid state transmitter is desired, it is usually necessary to combine the outputs of several FET amplifiers together by means of a microwave power combiner to attain a useful power output. Any such power combiner must provide a minimum of 10 dB isolation between its input and output ports in order to prevent the failure of a single amplifier from seriously degrading the performance of the remaining amplifiers and must be symmetrical to avoid phase and amplitude imbalances. In general, many known combiners are in the form of a planar array of T-junctions, thereby making the number of input ports equal to an integral power of two. Therefore, if, for example, the outputs of nine FETs are to be combined, an array of T-junctions having sixteen input ports would be required. In applications where space is at a premium, as, for example, in missile and aircraft installations, such a combiner is obviously undesirable. Furthermore, if such an array were to be used as a 9:1 power divider by applying power to the "input" port and taking power from the "output" ports, seven of the sixteen "output" ports would have to be terminated in matched loads which would dissipate 7/16ths of the applied power.
A known power divider, as is described in an article entitled "An N-Way Hybrid Power Divider" by E. J. Wilkinson, IRE Transactions Microwave Theory and Techniques, vol. MTT-13, pp. 116-118, January 1960, can provide an odd number of output ports. However, because the so-called "Wilkinson divider" employs circular symmetry, it also presents a serious packaging problem in that it cannot be realized in a planar structure, except for the case where N=2 (N being the number of output ports). A planar power combiner or divider having an odd number of input and output ports can be realized by combining a conventional T-junction power divider with a so-called "Split-T power divider" as described in an article entitled "Split-Tee Power Divider" by L. I. Parad and R. L. Moynihan, IEEE Transactions Microwave Theory and Techniques, vol. MTT-13, pp. 91-95, January 1965. Again, such a combination requires a substantial space for packaging and exhibits a large insertion loss.